Production of lower valent halides of ta, nb, ti and v



United States Patent PRODUCTIONVOF LOWER VALENT HALIDES oF Ta, Nb, Ti and v Stuart Sherman Carlton, Parma, Ohio, assignor, by mesne assignments, to Horizons Titanium Corporation, Princeton, N. L, acorporation of New Jersey No Drawing. Application November 30, 1954 Serial No. 472,255

10 Claims. (Cl. 204-64) This invention relates to the production of the polyvalent transitlon metals tantalum, niobium, titanium and vanadium. More particularly it relates to a process for producing halides of the transition metal in which the metal is present in a valencelower than the maximum valence exhibited by the metal.

In the copending application of John T. Burwell, Jr., and Quentin H. McKenna, Serial No. 398,193, there is described a method for producing a fused salt bath containing the above transition metals in a form capable of being cath'odically deposited by fused salt electrolysis in which either an alkali halide or an alkaline earth halide or both in further admixture with 5% to 50% of a solid transition metal halide is fused and there is then introduced into the fused salt a carbide of the transition metal (in solid form). Heating of the resultant solid containing fused salt is continued until the transition metal content of the solid product has been substantially completely converted to the transition metal halide in solution inthe fused salt by reaction with the fused halide salt-mass. The

resulting bath may then be electrolyzed to obtain .the

transition metal as a cathode deposit. This method finds carbide as asolid and the transition metal halide as --a gas.

A further advantage over the method disclosed in the aforesaid Burwell et al. application resides in the fact that a fused bath so prepared may contain substantially greater amounts of transition'metal in solution than baths prepared by the method'in the said copending application .Serial No. 398,l93. a

The method of the present invention is concerned with the production of the aforementioned fused salt bath of the Burwell, 'Jr., and McKenna application-containing the transition metal in a form-capable of being cathodically deposited-during fused salt electrolysis-of the type known as electrowinninng. My 'novel methodcomprises fusing either the alkali metal halide or theal-kaline earth metal halide or both. Solid pieces of transition metal carbide may be disposed in the fused bath, or the carbide may be continuously fed into the fused salt by suitable :means. The simple halide of the polyvalent transition metal is then bubbled as a gas into the fused salt mass. At theelevated. temperature of the fused salt-bath, approximately 900 C., the transitionmetal carbide and thegaseous halide react to'form with the originalfused bath a product which is capable of being electrolyzed in the fused state to effect cathodic deposition of the transition metal introduced into the fused bath by the aforesaid thermal step.

The method of the present invention is equally applibasket. divided form, it may either be charged directly into the "ice cable to the production of fused salt baths containing any of the polyvalent transition metals which can be electrodeposited by the method of the aforementioned 'Burwell and McKenna application. That is, the :present method is capable of producing equally useful fused salt baths containing a 'halide of any of the transition :metals titanium, niobium, tantalum and vanadium. Inasmuch as the production of such a fused salt bath containing a titanium hjalide is representative of the production of the corresponding baths containing the other aforementioned transition metal halides, the following discussion will bedirected simply to the titanium aspect of the invention in the interest of simplicity. However, it must be understood that 'what is said with respect to the production and use of the titanium bath applies withequal force and effect to the productionof corresponding fused salt baths containing the halides of each of the other transition metals niobium, tantalum and vanadium.

The fused bath in which the titanium halide is formed pursuant tomy invention may comprise one or more of the alkali-halides such as sodium and potassium chlorides,

bromides, iodides and fluorides or one or more of the alkaline earth metal halides such as calcium, barium, strontium and magnesium chlorides, bromides, iodides and fluorides, or mixtures of one or more of each of these alkali metal halides and alkaline earth metal halides.

The components of the fused salt bath should be of high purity and should be substantially completely anhydrous in order that extraneous-impurities, particularly oxygen,

in the electrodeposited transition metal which is produced by the subsequent electrolysisof the fused salt bath may be held to a minimum.

=Fusion of the components of the saltbath is carried out under conditions which will .insure the absence of atmospheric oxygen and moisture. Thus, Ihave found it advantageous to carryout this fusion in a closed reaction vessel in whichan inert atmosphere of argon or the like may bemaintained. The salt in the reaction vessel may be heated by any means which will not introduce impurities thereinto. For vexample, the exterior of the reaction vessel, which should be formed .of .a corrosion resistant materialsuch as graphite orthe like, may be heated by any suitable. means. On the other hand, the salt may be heated by electric resistance elements within the reaction vessel itself or by means of an alternating current passing through electrodes immersed in the salt. The salt should be heated to a temperature of at least 50 C., and advantageously about C., above its fusion point in order to insure adequate fluidity of the fused mass. In general, the fusion points of the various bath compositions described hereinbefore are such that an ultimate bath temperature of about 750 will insure the requisite bathifluidity. Temperatures from about 750 C. to '1300 C., and preferably within the-range of 800 C. to- 1200- C. are effective in promoting the reaction between. the simple titanium halide and the titanium carbide; higher temperatures within these ranges promoting more rapid and more complete reaction.

The titanium carbide may be introduced into the afore mentioned fused salt either in the form of relatively large lumps or in the form of smaller lumps of about 4 inch maximum dimension, or even in the form of finely divided particles. When the solidmaterial is introduced into the bath in relatively coarse form, it is advantageous to line "the graphite crucible containing the bath with rods of titanium carbide. It has also been found advantageous to suspend the lumps of carbide in the 'bath in agraphite When the solid material is employed in finely bath or it may be carried into the bath in a stream of carbide material is brought into the fused bath, :it has been found to react readily with the gaseous halide fed into the fused bath so that relatively little of the halide passes out of the bath.

Inthis reaction it is believed that the titanium component of the titanium carbide is oxidized and the titanium halide is correspondingly reduced to a lower valence titanium halide. For this reason, then the practice of this invention is restricted to the use of transition metals capable of existing in at least two different valence states in the form of halide salts, and this requirement is satisfiedonly by niobium (columbium), tantalum, titanium and vanadium. With each of these elements, its halide which is bubbled into the fused salt bath is the higher or highest valence form. The final bath composition contains the transition element in the form of one of its lower valence halides. It will be readily understood, therefore, that the amount of transition metal carbide which reacts with the transition metal higher valence halide is related to the amount of the higher valence halide available for reaction and to the difference in valence of the transition metal in the two forms of its halide, i. e., before and after reaction. In the case of titanium since the metal is capable of forming compounds in which it may be divalent, trivalent and tetravalent, the reaction desired conversion is effected by controlling the temperature. Thus at temperatures between about 750 C. and 850 C. each mole of simple tetrachloride in which the titanium has a valence of four will react with one-third mole of titanium carbide to form four-thirds (4/3) moles of the trichloride. At somewhat higher temperatures, between about 850 C. and 950 C., a mixture of the dichloride and trichloride is obtained while at temperatures above about 950 C. each mole of the titanium tetrachloride reacts with one mole of titanium carbide to form two moles of titanium dichloride.

The resulting fused salt bath is capable of being electrolyzed in the fused state with the resulting electrodeposition of the titanium content of the bath in the form of titanium metal. If the fused bath has been formed in the vessel which is to serve as the electrolytic cell, it may be electrolyzed directly. If the reaction vessel and the electrolytic cell are separate and distinct pieces of apparatus, the fused salt bath is transferred to the electrolytic cell, in which event it is desirable to remove any residual solid such as carbon or unreacted carbide by filtration. The transfer of the fused salt bath is effected by pipes of graphite or other inert material communicating between the thermal reactor and the electrolytic cell. The primary product of the electrolysis is titanium metal which is deposited on the cell cathode either as a recoverable titanium deposit or as a titanium cladding layer on a base metal cathode material. The halogen associated in the form of a salt with the titanium is liberated at the anode where it tends to combine with residual titanium carbide, if the electrolysis is conducted with titanium carbide present in the cell to form further lower valence halide. If the electrolysis is conducted in the absence of any substantial amount of titanium carbide, titanium tetrachloride is evolved at the anode and may be recovered quantitatively. The spent electrolytic bath may, if desired, be employed as the raw material fed into a reactor operated in the manner disclosed in the aforesaid Burwell and McKenna application, Serial No. 398,193, since it contains some dissolved titanium halide salt. The production of the titaniumcontaining bath and its subsequent electrolysis may also take place successively and repeatedly in a single vessel which thus serves both as the reactor and as the electrolytic cell. It will be understood that appropriate reflux equipment is provided for the recovery of any gases or vapors evolved from the cell.

The following specific examples are illustrative of the 'practice of this invention:

4 Example I Titanium carbide, prepared by heating a mixture of carbon and titanium dioxide to about 2000 C. under a vacuum and subsequently crushing and purifying the product, was mixed with methyl cellulose having a viscosity of 4000 centipoises in the proportions of 100 parts of 300 mesh (Tyler Standard) TiC to 1.5 parts of methyl cellulose. The mixture was shaped by extrusion into rods approximately in. in diameter and 6 in. long. After air drying for 24 hours, the rods were sintered in a vacuum at 2100 C. for a period of about one hour. The sintered TiC rods were disposed along the inner walls of a graphite crucible which, in this example, served successively as both the thermal reactor and the electrolytic cell.

The thermal reactor was provided with means to heat the charge and to maintain it at any desired temperature andwith an inlet and outlet for argon gas. The argon gas inlet was connected to a heated glass flask so that titanium tetrachloride vapor would be swept into the reactor by the argon gas which entered the reactor through a graphite bubbler tube. A graphite plate loosely covering the reactor permitted gas to enter or leave according to operating conditions.

The crucible was charged with sodium chloride and A heated under an argon atmosphere to about 850 C. to

fuse the salt. A graphite bubbler was introduced into the bottom of the fused salt and titanium tetrachloride was admitted to the cell at a rate of about 5 cc. per minute. Little fuming was observed until about 60 cc. had been added, after which dense fumes were evolved until 246 cc. had been added.

The bubbler was removed, a steel cathode was inserted and the bath electrolyzed with the crucible and titanium carbide rods serving as the anode. Electrolysis voltage ranged from 2.8 to 3.0 volts (below the minimum at which sodium chloride decomposes in cells of the type employed). Current was nevertheless extremely high, indicating the presence of reducible ions other than those of sodium chloride. The electrolysis was continued, under an argon atmosphere, until a total of 121 ampere hours input was supplied. A large uniform deposit of titanium was formed on the cathode; the yield, 28.6 grams of titanium, indicates a current efiiciency of about.40%.

Example 11 A second run was made on the bath of Example I with a fresh steel cathode. Electrolysis amperage was low and very little metal was deposited, indicating that the cathodically recoverable titanium values in the bath hadbeen exhausted.

Example III A third run was made on the bath of Example II. The cathode was withdrawn and the bubbler was reinserted into the bath. Titanium tetrachloride was bubbled into the bath. No fuming was observed until about 16 cc. had been added, after which fuming increased. After 300 cc. of titanium tetrachloride had been bubbled into the bath, the bubbler was removed and a steel cathode was inserted. The bath was electrolyzed with results similar to those in Example 1.

Example IV A fourth run was made on the bath of Example III without the further addition of titanium tetrachloride. Results were similar to those in Example 11.

At the end of this series of runs the fused salt residue was analyzed and found to contain 5.08% dissolved titanium. There was evidence of considerable attack on the titanium carbide rods. To ascertain the effect of carry ing out the electrolysis in the absence of titanium carbide, a slightly different procedure was followed in the example below.

Example V Instead of the non-gas tight cover on the cell of Example I, the cell now employed was arranged with a vacuum tight head equipped with a gate valve afiording connection with a sealed removal chamber. Means were provided to heat the cell to maintain the temperature and to admit and exhaust argon gas from the cell.

The graphite crucible was charged with 1500 grams of sodium chloride and heated to about 800 C. A perforated basket was positioned around the graphite bubbler and broken titanium carbide rods were disposed in the space between the bubbler and the basket. The flow of titanium tetrachloride was guided so that it followed a path downward through the graphite bubbler, and .out the tip of the bubbler, thence upwardly and outwardly through the broken TiC rods and the NaCl surrounding them, and thence out through the perforations in the basket into the fused bath. The celloutlet was connected to a reflux condenser but in the course of adding 120 grams of TiCl almost none of it passed out of the cell. On completing the addition of TiCl' the bubbler and the perforated basket containing the TiC were removed through the valved look.

A steel cathode was inserted and argon gas admitted to the cell. The bath was electrolyzed at 3.0 volts, current was about 20-30 amperes, but at 5.0 volts current was as high as 160 amperesl Electrolysis was conducted at 5 volts. Titanium was deposited at the cathode and fumes containing substantial amounts of titanium chloride were evolved from the anode region'of the cell and recovered by means of a condenser, provided for the purpose, After an input of 46 ampere hours, a slight voltage break occured, which is usually indicative of a sudden decrease in electrolyzable ions. The electrolysis was stopped. The cathode was withdrawn to cool in the gas tight chamber above the cell through which purified argon was kept flowing. After cooling in the removal chamber, the cathode deposit was broken from the cathode.

The separated cathode deposit was then dry mortared and soaked in 100 cc. of hot water containing .l-.l5% of H 0 This water was decanted and replaced by 1000 cc. of fresh similar H 0 hot water solution and this washing repeated for a total of six washings. The deposit was then wet mortared to break it down completely, following which the above-described washing step was repeated ten more times. After the last decantation, the cathode deposit was rinsed once in plain cold water and was then covered with cold concentrated HCl for 20 minutes. The acid was then rinsed off with water, the water was rinsed off with alcohol, and the finely divided solid product was then air dried in an oven. The yield was 11 ciently, employing inexpensive materials readily obtainable as articles of commerce. The simple halides of titanium, tantalum, vanadium and niobium may be reacted with the carbides of the same metals in a thermal reaction simultaneously with the electrolysis of a previously prepared path in separate and independently controlled reaction zones. Because the simple halides are employed in their gaseous form, contact with the carbides is rapid and intimate and the halides may be fully reacted in the thermal step.

As will be observed the electrolysis may take place either in the presence of titanium carbide or in its absence. In the latter case, the use of the graphite crucible as the anode offers the additional advantage that any oxygen present in the system will be removed as a carbon oxygen gas.

A further advantage of the method of my invention re i es in the r cove y of he simple alide n s bs anti lly quantitative amounts; as --.a product of the electrolysis carried out to effect deposition of the titanium metal.

Thus in the case of titanium employing titanium chloride as the simple halide, the system is virtually self sufficient as to titanium tetrachloride once the initial requirements have been supplied. I

I claim: Y

1. The method of forming a fused salt bath containing a lower-valent halide of a .polyvalent transition metal or the group consisting of titanium, niobium, tantalum, and vanadium and capable of being electrolyzed in the fused state with the resultingcathodic deposition of the transition metal which comprises: fusing at least one halide salt of the groupconsisting of alkali metal halides and alkaline earth metal halides, introducing into the resulting fused salt mass a carbide of the transition metal insolid form, thereafter introducinginto the mass a simple halide of the polyvalent transition metalin gaseous form thereby effecting a reaction between the simple halide and the carbide in the fused salt medium, recovering the resulting transition metal halide containing fused salt bath in which the transition metal is present in a lower valence form than its valance in the gaseous simple halide.

2. The method of recovering electrolytically a poly}.

valent transition metal of thegroup consisting of titanium, niobium, tantalum and vanadium which comprises: fusing at least one halide salt of the group consisting of alkali metal halides and alkaline earth metalhalides introducing into the resulting fused salt mass a carbide of the transition metal in solid form, thereafter introducing into the mass a simple halide of the polyvalent transition metal in gaseous form thereby effecting a reaction between the simple halide and the carbide in-the fused salt medium,

recovering the resulting transition metal halide containing fused salt bath in which the transition "metal is present in a lower valence form than the valence it exhibited in the gaseous simple halide, separating any unreacted solid carbide from the fused salt reaction product and recovering the transition metal as a cathode deposit and the simple halide as a gas evolved at an anode by passing an electrolyzing current between an anode and a cathode I and through said separated fused salt reaction product.

3. The method of forming a fused salt bath containing a lower-valent halide of titanium and capable of being electrolyzed in the fused state with the resulting cathodic deposition of the transition metal which comprises fusing at least one halide salt of the group consisting of alkali metal halides and alkaline earth metal halides, introducing into the resulting fused salt mass a carbide of titanium in solid form, thereafter introducing into the mass titanium tetrachloride, thereby effecting a reaction between the simple halide and the carbide in the fused salt medium, recovering the resulting fused salt bath containing the titanium in the form of a compound in which it has a valence less than four.

4. The method of electrolytically producing a polyvalent transition metal which comprises: fusing at least one halide salt of the group consisting of alkali metal halides and alkaline earth metal halides, introducing in solid form into the fused salt mass a carbide of a transition metal of the group consisting of titanium, niobium, tantalum and vanadium, thereafter introducing into the mass a simple halide of the same polyvalent transition metal in gaseous form, thereby effecting a reaction between the simple halide and the solid carbide in the fused salt medium, separating any unreacted solid carbide from the fused salt reaction product, electrolyzing the resultant fused salt bath by passing a current between an anode and a cathode immersed therein and recovering the polyvalent transition metal as a cathode deposit and the gaseous simple halide as a gas evolved at an anode.

5. The method of forming a fused salt bath containing a lower-valent halide of a polyvalent transition metal 7 of tl1 e "group consisting of'titanium, niobium, tantalum and van'adium and capable of being electrolyzed in the fused state with the resulting cathodic deposition of the transition metal which comprises: fusing at least one 'halide'salt of the group consisting of alkali metal halides and alkaline earth metal halides, introducing into the resulting fused salt mass a carbide of the transition metal in solid form, thereafter introducing into the mass 21 chloride of. the polyvalent transition metal in gaseous form in which'the valence of the transition metal is a higher valence exhibited by the said metal, thereby efiecting a reaction between the simple halide and the carbide 'in the fused salt medium, and recovering the resulting fused salt bath in which the transition metal is present 'in a lower valence form than the valence of the transition metal in the gaseous chloride.

6. The method of forming a fused salt bath containing a compound of titanium from the group consisting of divalent and trivalent titanium compounds which comprises fusing at least one halide salt of the group consisting of alkali metal halides and alkaline earth metal halides, introducing into the fused mass a carbide of titanium in solid form, thereafter introducing titanium tetrachloride into the mass as a gas, maintaining the aforesaid reactants at a temperature between about 750 C. and 1300 C. to effect a reaction between the tetrahalide and the carbide whereby a fused bath containing a titanium compound in which the valence of the titanium 'is less than four is formed.

7. The method of claim 6 in which the bath is maintained at about 800 C. to produce a bath containing a trivalent titanium compound. 7

8. The method of claim 6 in which the bath is maintained at about 950 C. to produce a bath containing a divalent titanium compound.

u 9. The method of producing a polyvalent transition metal of the group consisting of titanium, niobium, tan talum and vanadium which comprises:v fusing at least one halide salt of the group consisting of alkali metal halides and alkaline earth metal halides, introducing into the resultant fused mass a carbide of the transition metal in solid form, maintaining the bath at a temperature between about 750 C. and 1300 C., while introcarbide in a repetition of the process.

10. The method of claim 9 in which the simple halide is a chloride.

References Cited in the file of this patent UNITED STATES PATENTS Loonam Aug. 22, 1950 2,5 19,385 2,734,797 Skinner Feb. 14, 1956 FOREIGN PATENTS 682,919 Great Britain Nov. 19, 1952 708,595 Great Britain May 5, 1954 OTHER REFERENCES Electrolytic Preparation of Titanium, by Cordner and Worner, Australian Journal of Applied Science, vol. 2, No. 3, September 1951, pp. 358 to 367. 

2. THE METHOD OF RECOVERING ELECTROLYTICALLY A POLYVALENT TRANSITION METAL OF THE GROUP CONSISTING OF TITANIUM, NIOBIUM, TANTALUM AND VANADIUM WHICH COMPRISES: FUSING AT LEAST ONE HALIDE SALT OF THE GROUP CONSISTING OF ALKALI METAL HALIDES AND ALKALINE EARTH METAL HALIDES INTRODUCING INTO THE RESULTING FUSED SALT MASS A CARBIDE OF THE TRANSITION METAL IN SOLID FORM, THEREAFTER INTRODUCING INTO THE MASS A SIMPLE HALIDE OF THE POLYVENT TRANSITION METAL IN GASEOUS FORM THEREBY EFFECTING A REACTION BETWEEN THE SIMPLE HALIDE AND THE CARBIDE IN THE FUSED SALT MEDIUM, RECOVERING THE RESULTING TRANSITION METAL HALIDE CONTAINING FUSED SALT BATH IN WHICH THE TRANSITION METAL IS PRESENT IN A LOWER VALENCE FORM THAN THE VALENCE IT EXHIBITED IN THE GASEOUS SIMPLE HALIDE, SEPARATING ANY UNREACTED SOLID CARBIDE FROM THE FUSED SALT REACTION PRODUCT AND RECOVERING THE TRANSITION METAL AS A CATHODE DEPOSIT AND THE SIMPLE HALIDE AS A GAS EVOLVED AT AN ANODE BY PASSING AN ELECTROLYZING CURRENT BETWEEN AN ANODE AND A CATHODE AND THROUGH SAID SEPARATED FUSED SALT REACTION PRODUCT. 